In an operation to record time-series information such as video and audio information onto a recording medium such as a disk, a tape or a semiconductor memory, for example, the time-series information is generally compressed to allow the time-series information continuing over a long period of time to be recorded in a limited area in the recording medium.
As the conventional method of compressing data, an MPEG (Moving Picture Experts Group) method is used widely.
The MPEG method is a technique for compressing data by using predictive coding based on correlations between pieces of information in video frames or video fields and utilizing a DCT (Discrete Cosine Transform) process. The video frames or the video fields are decoding/reproduction units of video information.
In the MPEG method, a picture, which can be a frame or a field, can have one of three types, i.e. an I picture, a P picture and a B picture. In order to simplify the explanation, however, only the technical term ‘frame’ is used as the decoding/reproduction unit of video information in the following description.
The I picture is an intra-coded picture obtained as a result of compression and coding only the data in one frame of the picture itself. The P picture is a forward-direction predictive-coded picture obtained as a result of compression and coding of data on the basis of a correlation with a picture frame preceding the frame of the P picture. The B picture is a both-direction predictive-coded picture obtained as a result of compression and coding of data on the basis of correlations with picture frames succeeding and preceding the frame of the B picture.
In the MPEG method, a so-called GOP (Group of Pictures) unit including a plurality of frames is used as a read/write unit, which is a unit of data read-out from and written into a recording medium. Typical GOPs are shown in FIGS. 9A and 9B.
As shown in FIGS. 9A and 9B, a GOP in the MPEG method includes at least one I picture. This is because an image cannot be decoded on the basis of only P and B pictures. By including an I picture in a GOP in this way, a random access to any GOP can be made.
I and P pictures are coded in the same order as the order of the original frames. However, a B picture must be coded after I and P pictures are coded. If this encoding order is to be taken into consideration, in an MPEG encoder, frames are rearranged from the original order shown in FIG. 9A into a new order shown in FIG. 9B before the frames are compressed and coded. For details, refer to Japanese Patent Laid-Open No. Hei8-214265.
To put it in detail, as shown by an arrow in FIG. 9A, a P picture is subjected to predictive coding using an I or P picture preceding the P picture being coded. On the other hand, a B picture is subjected to predictive coding using an I or P picture preceding the B picture and an I or P picture succeeding the B picture. That is to say, the B picture is sandwiched by the I or P picture preceding the B picture and the I or P picture succeeding the B picture.
Since a B picture is encoded-by using an I or P picture succeeding the B picture as described above, in the new order shown in FIG. 9B, the B picture is placed after the I or P picture originally succeeding the B picture before the arrangement.
In addition, as will be described later, management information for decoding and reproduction is added to each decoding/reproduction unit (that is, each picture unit) of the compressed-coded image data and recorded onto a recording medium along with the coded image data. Then, in an operation to reproduce image data coded by adoption of the MPEG method, the management information for decoding and reproduction is extracted from the recorded data and, on the basis of the management information, an image output is controlled in reproduced picture units and the order of the frames is restored to the original one.
By the way, in a digital camera capable of taking a picture of not only a still picture but also a moving picture, the MPEG method is also adopted as a data compression method. The digital camera is capable of offering more convenience to the user if an image pickup time and image pickup conditions can be recorded onto a recording medium as additional information. The image pickup conditions include a diaphragm-setting state, an exposure value and a white-balance state.
In particular, if the additional information such as an image pickup time and image pickup conditions can be recorded for an image of each frame, the user will be capable of knowing how the picture of each frame was taken and enjoy more convenience. In addition, by referring to the additional information for the image of each frame in an image reproduction process or an image-editing process, the reproduction quality can be improved and a fine editing process can be carried out. As a result, it is expected that the present invention can be applied to a variety of applications.
In the transmission format of data recorded by adoption of the MPEG method, however, there is no proposed policy as to how additional information for video and audio data is to be recorded (and transmitted). Thus, there is a technological problem as to how additional information is to be added in a state allowing the information to be used with a high degree of convenience.
In this case, if a GOP serving as a unit of data read out from and written into a recording medium includes a plurality of picture frames each used as a decoding/reproduction unit as is the case with the MPEG method described above, in an attempt to record additional information for data of each decoding/reproduction unit, a technique as to how the additional information is associated with the data of each decoding/reproduction unit is important.
In particular, when frames in a GOP serving as a read/write unit in the MPEG method are rearranged in a coding process prior to a recording process into a new order shown in FIG. 9B as described earlier, there is raised a problem that it becomes difficult to associate the data of each decoding/reproduction unit with the additional information.
It is thus an object of the present invention addressing the problems described above to provide a recording method capable of associating additional information for data of each decoding/reproduction unit with the unit with a high degree of reliability even if a read/write unit of data read out from and written into a recording medium includes a plurality of aforementioned decoding/reproduction unit and provide a recording apparatus for the recording method.